Systems and methods of monitoring autoregulation

ABSTRACT

A system for monitoring autoregulation includes an oxygen saturation sensor configured to obtain an oxygen saturation signal indicative of an oxygen saturation of a patient. The system also includes a controller having a processor configured to receive a blood pressure signal indicative of a blood pressure of the patient and the oxygen saturation signal, determine a change in the oxygen saturation signal and a change in the blood pressure signal over a period of time, and provide an indication that the patient&#39;s autoregulation is intact if the oxygen saturation changes by more than an oxygen saturation threshold and if the blood pressure changes by less than a blood pressure threshold during the period of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of ProvisionalApplication No. 62/362,325, entitled “SYSTEMS AND METHODS OF MONITORINGAUTOREGULATION USING GRADIENT MATCHING,” filed Jul. 14, 2016, andProvisional Application No. 62/362,329, entitled “SYSTEM AND METHOD OFMONITORING AUTOREGULATION,” filed Jul. 14, 2016, which are hereinincorporated by reference in their entirety for all purposes.

BACKGROUND

The present disclosure relates generally to medical devices and, moreparticularly, to systems and methods of monitoring autoregulation.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, medical professionals often desire to monitorcertain physiological parameters of their patients. In some cases,clinicians may wish to monitor a patient's autoregulation.Autoregulation is a physiological process that attempts to maintain anoptimal cerebral blood flow to supply appropriate levels of oxygen andnutrients to the brain. During autoregulation, cerebral arteriolesdilate or constrict to maintain optimal blood flow. For example, ascerebral pressure decreases, cerebral arterioles dilate in an attempt tomaintain blood flow. As cerebral pressure increases, cerebral arteriolesconstrict to reduce the blood flow that could cause injury to the brain.If the patient's autoregulation process is not functioning properly, thepatient may experience inappropriate cerebral blood flow, which may havenegative effects on the patient's health. In particular, a drop incerebral blood flow may cause ischemia, which may result in tissuedamage or death of brain cells. An increase in cerebral blood flow maycause hyperemia, which may result in swelling of the brain or edema.

Some existing systems for monitoring autoregulation may determine apatient's autoregulation status based on a correlation coefficient.However, such a correlation coefficients may be subject to varioussources of error. Furthermore, many data points may be required toreliably calculate such correlation coefficients. Accordingly, anextended period of time (e.g., several minutes, or even hours) may passbefore such systems are able to provide a reliable indication of thepatient's autoregulation status. In certain clinical settings, theextended time for determining whether the patient's autoregulation isintact or impaired may affect patient care and outcomes. Therefore,systems and methods for efficiently and reliably determining thepatient's autoregulation status are provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the disclosed techniques may become apparent upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 is a block diagram of an embodiment of a system for monitoring apatient's autoregulation;

FIG. 2 is an example of a graph illustrating a linear correlationbetween oxygen saturation values and blood pressure values;

FIG. 3 is an example of a graph illustrating a cerebral oximetry index(COx) over a range of blood pressures;

FIG. 4 is a table illustrating indications of autoregulation statusbased on various changes in oxygen saturation and blood pressure over aperiod of time;

FIG. 5 is another table illustrating indications of autoregulationstatus based on various changes in oxygen saturation and blood pressureover a period of time;

FIG. 6 is a process flow diagram of a method of monitoringautoregulation by comparing a change in blood pressure to a threshold,in accordance with an embodiment;

FIG. 7 is a process flow diagram of a method of monitoringautoregulation by comparing a change in blood pressure and a change inoxygen saturation to respective thresholds, in accordance with anembodiment;

FIG. 8 is a process flow diagram of a method of monitoringautoregulation based on a relationship between gradients of oxygensaturation and blood pressure, in accordance with an embodiment;

FIG. 9A is an example of a graph illustrating an oxygen saturationsignal and a blood pressure signal over a period of time;

FIG. 9B is an example of a graph illustrating a gradient of oxygensaturation and a gradient of blood pressure over the period of timebased on the signals of FIG. 9A;

FIG. 9C is an example of a graph illustrating autoregulation status overthe period of time based on the gradients of FIG. 9B;

FIG. 10 is a process flow diagram of another method of monitoringautoregulation based on prior autoregulation data, in accordance with anembodiment;

FIG. 11 is an example of a graph that may be generated via the method ofFIG. 10, wherein the graph illustrates autoregulation function acrossvarious blood pressures; and

FIG. 12 is a process flow diagram of another method of monitoringautoregulation by updating a correlation coefficient based on priorautoregulation data, in accordance with an embodiment.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present techniques will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers'specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

A physician may monitor a patient's autoregulation through the use ofvarious monitoring devices and systems. In some cases, a system mayinclude a controller (e.g., an electronic controller having a processorand a memory) that is configured to monitor a patient's autoregulationby based on measurements of the patient's blood pressure (e.g., meanarterial blood pressure) and measurements of the patient's oxygensaturation (e.g., regional oxygen saturation). In some cases, a cerebraloximetry index (COx) may be derived based at least in part on a linearcorrelation between the patient's blood pressure and oxygen saturation.However, as discussed in more detail below, the COx may not accuratelyreflect the patient's autoregulation status during periods of time whenthe patient's blood pressure is generally stable.

In view of the foregoing, during autoregulation monitoring, it may bedesirable to determine whether the patient's blood pressure varies bymore than a threshold (e.g., a blood pressure threshold, such asapproximately 1, 2, 3, 4, or 5 millimeters of mercury [mmHg]) over aperiod of time (e.g., approximately 0.5, 1, 2, 3, 4, 5, or moreminutes). In certain embodiments, the controller may calculate the COxonly if the patient's blood pressure varies by more than the thresholdover the period of time. In certain embodiments, the controller maydiscard the COx and/or may not provide (e.g., display) the COx if thepatient's blood pressure varies by less than the threshold over theperiod of time. For example, a change in the patient's blood pressurethat exceeds the threshold over the period of time may cause thecontroller to calculate and/or to provide an indication of the COx,while a change in the patient's blood pressure that is less than thethreshold over the period of time may block the controller fromcalculating and/or displaying the indication of the COx. In certainembodiments, the controller may display a prior COx (e.g., a most recentCOx value, a most recent COx value at the same blood pressure, or anaverage or a weighted average of previously calculated COx values at thesame blood pressure) if the patient's blood pressure varies by less thanthe threshold.

In certain embodiments, the controller may determine whether thepatient's blood oxygen saturation varies by more than a threshold (e.g.,an oxygen saturation threshold, such as approximately 1, 2, 3, 4, or 5percent) over the period of time. In some such cases, the controller maydetermine and/or provide an indication (e.g., via a display or aspeaker) that the patient's autoregulation is intact if the bloodpressure varies by less than the blood pressure threshold and if theoxygen saturation varies by more than the oxygen saturation thresholdover the period of time. For example, a change in the patient's bloodpressure that is less than the blood pressure threshold over the periodof time in combination with a change in the patient's oxygen saturationthat exceeds the oxygen saturation threshold over the period of time maycause the controller to determine and/or to provide an indication thatthe patient's autoregulation is intact. Thus, the disclosed systems andmethods may provide improved patient monitoring and patient care.

FIG. 1 illustrates an embodiment of a system 10 configured to monitorautoregulation. As shown, the system 10 includes a blood pressure sensor12, an oxygen saturation sensor 14 (e.g., a regional oxygen saturationsensor), a controller 16 (e.g., an electronic controller), and an outputdevice 18. The blood pressure sensor 12 may be any sensor or deviceconfigured to obtain the patient's blood pressure (e.g., mean arterialblood pressure). For example, the blood pressure sensor 12 may include ablood pressure cuff for non-invasively monitoring blood pressure or anarterial line for invasively monitoring blood pressure. In certainembodiments, the blood pressure sensor 12 may include one or more pulseoximetry sensors. In some such cases, the patient's blood pressure maybe derived by processing time delays between two or more characteristicpoints within a single plethysmography (PPG) signal obtained from asingle pulse oximetry sensor. Various techniques for deriving bloodpressure based on a comparison of time delays between certain componentsof a single PPG signal obtained from a single pulse oximetry sensor isdescribed in U.S. Publication No. 2009/0326386, entitled “Systems andMethods for Non-Invasive Blood Pressure Monitoring,” the entirety ofwhich is incorporated herein by reference. In other cases, the patient'sblood pressure may be continuously, non-invasively monitored viamultiple pulse oximetry sensors placed at multiple locations on thepatient's body. As described in U.S. Pat. No. 6,599,251, entitled“Continuous Non-invasive Blood Pressure Monitoring Method andApparatus,” the entirety of which is incorporated herein by reference,multiple PPG signals may be obtained from the multiple pulse oximetrysensors, and the PPG signals may be compared against one another toestimate the patient's blood pressure. Regardless of its form, the bloodpressure sensor 12 may be configured to generate a blood pressure signalindicative of the patient's blood pressure (e.g., arterial bloodpressure) over time. As discussed in more detail below, the bloodpressure sensor 12 may provide the blood pressure signal to thecontroller 16 or to any other suitable processing device to enableevaluation of the patient's autoregulation status.

As shown, the oxygen saturation sensor 14 may be a regional oxygensaturation sensor configured to generate an oxygen saturation signalindicative of blood oxygen saturation within the venous, arterial, andcapillary systems within a region of the patient. For example, theoxygen saturation sensor 14 may be configured to be placed on thepatient's forehead and may be used to calculate the oxygen saturation ofthe patient's blood within the venous, arterial, and capillary systemsof a region underlying the patient's forehead (e.g., in the cerebralcortex). In such cases, the oxygen saturation sensor 14 may include anemitter 20 and multiple detectors 22. The emitter 20 may include atleast two light emitting diodes (LEDs), each configured to emit atdifferent wavelengths of light, e.g., red or near infrared light. Insome embodiments, light drive circuitry (e.g., within a monitor orwithin the sensor 14) may provide a light drive signal to drive theemitter 20 and to cause the emitter 20 to emit light. In one embodiment,the LEDs of the emitter 20 emit light in the range of about 600 nm toabout 1000 nm. In a particular embodiment, one LED of the emitter 20 isconfigured to emit light at about 730 nm and the other LED of theemitter 20 is configured to emit light at about 810 nm. One of thedetectors 22 is positioned relatively “close” (e.g., proximal) to theemitter 20 and one of the detectors 22 is positioned relatively “far”(e.g., distal) from the emitter 22. Light intensity of multiplewavelengths may be received at both the “close” and the “far” detectors22. For example, if two wavelengths are used, the two wavelengths may becontrasted at each location and the resulting signals may be contrastedto arrive at a regional saturation value that pertains to additionaltissue through which the light received at the “far” detector passed(tissue in addition to the tissue through which the light received bythe “close” detector passed, e.g., the brain tissue), when it wastransmitted through a region of a patient (e.g., a patient's cranium).Surface data from the skin and skull may be subtracted out, to generatea regional oxygen saturation (rSO₂) signal for the target tissues overtime. As discussed in more detail below, the oxygen saturation sensor 14may provide the regional oxygen saturation signal to the controller 16or to any other suitable processing device to enable evaluation of thepatient's autoregulation status. While the depicted oxygen saturationsensor 14 is a regional saturation sensor, the sensor 14 may be a pulseoximetry sensor configured to obtain the patient's oxygen saturation ormay be any suitable sensor configured to provide a signal indicative ofthe patient's blood flow. For example, the sensor 14 may be configuredto emit light at a single wavelength (e.g., an isobestic wavelength) andto provide a signal indicative of blood flow.

In operation, the blood pressure sensor 12 and the oxygen saturationsensor 14 may each be placed on the same or different parts of thepatient's body. Indeed, the blood pressure sensor 12 and the oxygensaturation sensor 14 may in some cases be part of the same sensor orsupported by a single sensor housing. For example, the blood pressuresensor 12 and the oxygen saturation sensor 14 may be part of anintegrated oximetry system configured to non-invasively measure bloodpressure (e.g., based on time delays in a PPG signal) and regionaloxygen saturation. One or both of the blood pressure sensor 12 or theoxygen saturation sensor 14 may be further configured to measure otherparameters, such as hemoglobin, respiratory rate, respiratory effort,heart rate, saturation pattern detection, response to stimulus such asbispectral index (BIS) or electromyography (EMG) response to electricalstimulus, or the like. While an exemplary system 10 is shown, theexemplary components illustrated in FIG. 1 are not intended to belimiting. Indeed, additional or alternative components and/orimplementations may be used.

As noted above, the blood pressure sensor 12 may be configured toprovide the blood pressure signal to the controller 16, and the oxygensaturation sensor 14 may be configured to provide the oxygen saturationsignal to the controller 16. In certain embodiments, the controller 16is an electronic controller having electrical circuitry configured toprocess the various received signals. In particular, the controller 16may be configured to process the blood pressure signal and the oxygensaturation signal to evaluate the patient's cerebral autoregulationstatus. Although the blood pressure sensor 12 and the oxygen saturationsensor 14 may be configured to provide their respective signals or datadirectly to the controller 16, in certain embodiments, the signals ordata obtained by the blood pressure sensor 12 and/or the oxygensaturation sensor 14 may be provided to one or more intermediateprocessing devices (e.g., specialized monitor, such as a blood pressuremonitor or an oxygen saturation monitor, or the like), which may in turnprovide processed signals or data to the controller 16. In someembodiments, the controller 16 may be part of a specialized monitor,such as a blood pressure monitor, an oxygen saturation monitor, amedical monitor configured to monitor physiological characteristics, orthe like.

In the illustrated embodiment, the controller 16 includes a processor 24and a memory device 26. The controller 16 may also include one or morestorage devices. The processor 24 may be used to execute software, suchas software for carrying out any of the techniques disclosed herein,such as processing the blood pressure signals and/or oxygen saturationsignals, determining changes in the blood pressure signals and/or oxygensaturation signals, comparing the changes to thresholds, determiningmetrics (e.g., COx) indicative of the patient's autoregulation status,carrying out appropriate actions (e.g., providing indications on adisplay), and so forth. Moreover, the processor 24 may include multiplemicroprocessors, one or more “general-purpose” microprocessors, one ormore special-purpose microprocessors, and/or one or more applicationspecific integrated circuits (ASICS), or some combination thereof. Forexample, the processor 24 may include one or more reduced instructionset (RISC) processors.

The memory device 26 may include a volatile memory, such as randomaccess memory (RAM), and/or a nonvolatile memory, such as ROM. Thememory device 26 may include one or more tangible, non-transitory,machine-readable media collectively storing instructions executable bythe processor 24 to perform the methods and control actions describedherein. Such machine-readable media can be any available media that canbe accessed by the processor 24 or by any general purpose or specialpurpose computer or other machine with a processor. The memory device 26may store a variety of information and may be used for various purposes.For example, the memory device 26 may store processor-executableinstructions (e.g., firmware or software) for the processor 24 toexecute, such as instructions for carrying out any of the techniquesdiscloses herein, such as processing the blood pressure signal and/orthe oxygen saturation signal, determining changes in the blood pressuresignals and/or oxygen saturation signals, comparing the changes tothresholds, determining metrics (e.g., COx) indicative of the patient'sautoregulation status, carrying out appropriate actions (e.g., providingindications on a display), and so forth. The storage device(s) (e.g.,nonvolatile storage) may include read-only memory (ROM), flash memory, ahard drive, or any other suitable optical, magnetic, or solid-statestorage medium, or a combination thereof. The storage device(s) maystore data (e.g., the blood pressure signal, the oxygen saturationsignal, the COx, etc.), instructions (e.g., software or firmware forprocessing the blood pressure signal and/or the oxygen saturationsignal, determining changes in the blood pressure signals and/or oxygensaturation signals, comparing the changes to thresholds, determiningmetrics (e.g., COx), carrying out appropriate actions, and so forth),predetermined thresholds, and any other suitable data.

As shown, the system 10 includes the output device 18. In someembodiments, the controller 16 may be configured to provide signalsindicative of the patient's autoregulation status to the output device18. As discussed in more detail below, the controller 16 may beconfigured to generate an alarm signal indicative of the patient'sautoregulation status and to provide the alarm signal to the outputdevice 18. The output device 18 may include any device configured toreceive signals (e.g., the signal indicative of the patient'sautoregulation status, the alarm signal, or the like) from thecontroller 16 and visually and/or audibly output information indicativeof the patient's autoregulation status (e.g., the COx, prior COx values,the COx signal, an alarm, a symbol, a text message, or the like). Forinstance, the output device 18 may include a display configured toprovide a visual representation of the patient's autoregulation statusand/or the COx, as determined by the controller 16. Additionally oralternatively, the output device 18 may include an audio deviceconfigured to provide sounds in accordance with the patient'sautoregulation status and/or the COx. The output device 18 may be anysuitable device for conveying such information, including a computerworkstation, a server, a desktop, a notebook, a laptop, a handheldcomputer, a mobile device, or the like. In some embodiments, thecontroller 16 and the output device 18 may be part of the same device orsupported within one housing (e.g., a computer or monitor).

As noted above, in some embodiments, the controller 16 may be configuredto determine a cerebral oximetry index (COx) based on the blood pressuresignal and the oxygen saturation signal. The controller 16 may derivethe COx by determining a linear correlation between blood pressuremeasurements and oxygen saturation measurements. The linear correlationmay be based on a Pearson coefficient, for example. The Pearsoncoefficient may be defined as the covariance of the measured bloodpressure (e.g., mean arterial blood pressure) and oxygen saturationdivided by the product of their standard deviations. The result of thelinear correlation may be a regression line between oxygen saturationmeasurements and blood pressure measurements.

With the foregoing in mind, FIG. 2 is an example of a graph 40illustrating a linear correlation between blood pressure measurements 42(e.g., mean arterial blood pressure measurements) and oxygen saturationmeasurements 44. As noted above, the result of the linear correlationmay be a regression line 46 between the blood pressure measurements 42and the oxygen saturation measurements 44. In the illustrated example,the slope of the regression line 46 is negative and, thus, the COx valueis between −1 and 0. When the slope of the regression line 46 ispositive, the COx value is between 0 and 1.

During periods of varying blood pressure (e.g., changes of at leastapproximately 1, 2, 3, 4, or 5 millimeters of mercury [mmHg] over a timewindow of approximately 0.5, 1, 2, 3, 4, 5, or more minutes), the COxvalue may provide an accurate and/or useful indication of vascularreactivity, which is related to cerebral blood vessels' ability tocontrol proper blood flow, via vasoconstriction (a narrowing of theblood vessel) and/or vasodilation (expansion of the blood vessel), forexample. Thus, in such circumstances, the COx value may also begenerally indicative of whether the patient's autoregulation isimpaired. For example, in such circumstances, a COx value between −1 and0 (e.g., a regression line with a relatively flat or negative slope;regional oxygen saturation remains the same or decreases after bloodpressure increases) may suggest that cerebral autoregulation is workingproperly, while a COx value between 0 and 1 (e.g., a regression linewith a positive slope; regional oxygen saturation increases after bloodpressure increases) or above some predetermined threshold between 0 and1 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9) may suggestthat the cerebral autoregulation is impaired.

However, the COx value may not accurately reflect the patient'sautoregulation status when the patient's blood pressure is generallystable (e.g., changes of less than approximately 1, 2, 3, 4, or 5 mmHgover a time window of approximately 0.5, 1, 2, 3, 4, 5, or moreminutes). FIG. 3 illustrates a graph 48 of COx values 50 over a range ofblood pressures 52. As shown, certain COx values 50 identified by a line54 are caused by noise due to changes in oxygen saturation duringperiods of generally stable blood pressure. In certain embodiments ofthe present disclosure, such COx values 50 (e.g., the COx values 50within the box 54, or those COx values 50 calculated over a time windowin which blood pressure 52 is generally stable) are not calculated, arenot used to assess the patient's autoregulation status, and/or are notprovided (e.g., are not output to an operator via the output device 18).

Thus, in certain embodiments, the controller 16 may be configured todetermine whether the patient's blood pressure varies by more than athreshold (e.g., a blood pressure threshold, such as approximately 1, 2,3, 4, or 5 mmHg) over a period of time (e.g., a time window ofapproximately 0.5, 1, 2, 3, 4, 5, or more minutes). In certainembodiments, the controller 16 may calculate the COx only if thepatient's blood pressure varies by more than the threshold over theperiod of time. In certain embodiments, the controller 16 may discardthe COx calculated over the period of time and/or may not provide anindication of the COx and/or determine the patient's autoregulationstatus when blood pressure varies by less than the threshold over theperiod of time. In certain embodiments, the controller 16 may provide anindication of a prior COx value (e.g., a most recent COx value, a mostrecent COx value at the same blood pressure, or an average or a weightedaverage of previously calculated COx values at the same blood pressure)and/or an indication of a prior autoregulation status if the patient'sblood pressure varies by less than the threshold over the period oftime. For example, the controller 16 may output (e.g., cause display of)the prior COx value until the blood pressure varies by more than thethreshold. In some such embodiments, the controller 16 may provide anindication that the COx value and/or autoregulation status is beingheld, that the prior COx value and/or autoregulation status is beingprovided, and/or that the COx value and/or the autoregulation status isnot being calculated. In some such embodiments, the controller 16 mayprovide an indication of a time that the prior COx value and/orautoregulation status has been held and/or a time that the COx valueand/or the autoregulation status has not been calculated. In someembodiments, the controller 16 may provide an alert if an extendedperiod of time (e.g., more than 5, 10, 15, 20, 30, or more minutes) haspassed since the blood pressure has changed by more than the threshold(i.e., since the COx value and/or autoregulation status has beencalculated and/or provided). Such an alert may provide an indication ofthe reliability of the provided COx value and/or autoregulation status.In some embodiments, the controller 16 may be configured to determineand/or to provide an indication of the reliability of the provided COxvalue and/or autoregulation status. For example, the controller 16 mayprovide a number (e.g., 1 to 10) or colored indicators indicative of areliability of the provided COx value and/or autoregulation status basedon a length of time since the COx and/or the autoregulation status wascalculated. In this way, the changes may enable the controller 16 toidentify portions of the COx signal that are adversely affected by noiseor processing errors, and which are therefore unreliable. In certainembodiments, the controller 16 may be configured to remove or discardthe unreliable portions of the COx signal and/or take other appropriateremedial actions, as discussed in more detail below.

FIG. 4 is a table 60 illustrating indications of autoregulation functionthat may be provided by the controller 16 based on various changes inoxygen saturation and blood pressure. As shown in rows 62, 64, if theblood pressure changes by more than the threshold over the period oftime, the autoregulation status may be determined and/or provided by thecontroller 16. For example, the controller 16 may calculate the COxbased on a relationship between the blood pressure and the oxygensaturation and determine the autoregulation status based on the COx.However, as shown in row 66, if the blood pressure is generally stableover the period of time, the controller 16 may not determine the COxand/or the patient's autoregulation status. As discussed above, in someembodiments, if the blood pressure is generally stable over the periodof time, the controller 16 may provide the prior COx and/orautoregulation status.

In certain embodiments, the controller 16 may be configured to determineand/or to provide information related to the patient's autoregulationstatus while the patient's blood pressure is generally stable. With theforegoing in mind, FIG. 5 is a table 70 illustrating indications ofautoregulation function that may be provided by the controller 16 basedon various changes in oxygen saturation and blood pressure. As shown inrows 72, 74, if the blood pressure changes by more than the thresholdover the period of time, the autoregulation status may be determinedand/or provided by the controller 16. For example, the controller 16 maycalculate the COx based on a relationship between the blood pressure andthe oxygen saturation and determine the autoregulation status based onthe COx. As discussed above, if the blood pressure is generally stableover the period of time, the controller 16 may not determine the COx.However, as shown in boxes 78, 80 of row 76, if the blood pressure isgenerally stable over the period of time and if the oxygen saturationvaries by more than a threshold (e.g., an oxygen saturation threshold,such as approximately 1, 2, 3, 4, or 5 percent) over the period of time,the controller 16 may determine and/or provide an indication that thepatient's autoregulation is intact. In certain embodiments, as shown inbox 82 of row 76, if both the blood pressure and the oxygen saturationare generally stable over the period of time, the controller 16 may notdetermine the patient's autoregulation status. In some such cases, thecontroller 16 may provide the prior autoregulation status or anindication that the patient's autoregulation status has not beendetermined, for example.

Accordingly, with reference to the system 10 of FIG. 1, in certainembodiments, the controller 16 may determine whether the patient's bloodoxygen saturation varies by more than a threshold (e.g., an oxygensaturation threshold, such as approximately 1, 2, 3, 4, or 5 percent)over the period of time. In some embodiments, the controller 16 maydetermine that the patient's autoregulation is intact if the bloodpressure varies by less than the blood pressure threshold and if theoxygen saturation varies by more than the oxygen saturation thresholdover the period of time. In certain embodiments, the controller 16 maybe configured to provide an indication (e.g., via a display or aspeaker) that the patient's autoregulation is intact, if the bloodpressure varies by less than the threshold and if the oxygen saturationvaries by more than the threshold. Such characteristics may indicatethat the patient's blood flow (e.g., as indicated by the oxygensaturation signal) does not correlate with or is not driven by thepatient's blood pressure, but rather, is controlled by the patient'sautoregulation system to maintain appropriate blood flow.

In some embodiments, if the blood pressure varies by less than thethreshold and if the oxygen saturation varies by more than thethreshold, the controller 16 may automatically extend the period of time(e.g., continue to collect data for an additional 0.5, 1, 2, 3, 4, or 5minutes) prior to determining and/or providing an indication that thepatient's autoregulation is intact. In some embodiments, if the bloodpressure varies by less than the threshold and if the oxygen saturationvaries by more than the threshold, the controller 16 may provide anindication of the reliability of the provided intact autoregulationstatus. For example, the controller 16 may determine and/or provide anindication that the intact autoregulation status has a relatively lowerreliability due to the absence of a COx value at the generally stableblood pressure, as compared to periods of varying blood pressure. Forexample, the controller 16 may provide a number (e.g., 1 to 10) orcolored indicator indicative of a reliability of the providedautoregulation status. In some embodiments, if the blood pressure variesby less than the threshold and if the oxygen saturation varies by lessthan the threshold (i.e., both parameters are generally stable), thecontroller 16 may provide an indication that the COx and/or theautoregulation status cannot be reliably determined and/or may providean indication of a prior COx value and/or a prior autoregulation status,in the manner discussed above.

In some embodiments, if the blood pressure varies by less than thethreshold and if the oxygen saturation varies by more than thethreshold, the controller 16 may compare changes in the patient'sregional oxygen saturation signal (rSO₂) and arterial oxygen saturationsignal (SpO₂), and the controller 16 may block output of the indicationthat patient's autoregulation is intact if both the patient's rSO2 andthe SpO2 change by a threshold amount in the same direction (e.g., bothincrease or both decrease) over the period of time. It should beunderstood that the thresholds and/or the period of time may bepredetermined (e.g., stored in the memory device 26 and accessed by theprocessor 24) and/or may be selected by a user (e.g., via inputscommunicatively coupled to the controller 16). Additionally, althoughcertain examples provided herein utilize the COx, in some embodiments,the techniques may be adapted for use with other metrics or measures ofautoregulation, such as a mean velocity index (Mx) and/or a pressurereactivity index (PRx) and/or a vascular reactivity index (HVx) and/or agradient-based metric, which is discussed in more detail below.

FIGS. 6 and 7 are flow charts illustrating methods for monitoringautoregulation based on a change in blood pressure and/or a change inoxygen saturation, in accordance with the present disclosure. Themethods disclosed herein include various steps represented by blocks. Itshould be noted any of the methods provided herein may be performed asan automated procedure by a system, such as system 10. In particular,some or all of the steps of the methods may be implemented by thecontroller 16 (e.g., the processor 24 of the controller 16) of FIG. 1,for example, to determine the patient's autoregulation status and/or totake an appropriate action (e.g., output a visual or audible indicationof the autoregulation status, or the like). Although the flow chartsillustrate the steps in a certain sequence, it should be understood thatthe steps may be performed in any suitable order and certain steps maybe carried out simultaneously, where appropriate. Additionally, steps ofthe various methods disclosed herein may be combined in any suitablemanner and steps may be added or omitted. Further, certain steps orportions of the methods may be performed by separate devices. Forexample, a first portion of a method may be performed by the controller16, while a second portion of the method may be performed by the sensor14. In addition, insofar as steps of the methods disclosed herein areapplied to received signals, it should be understood that the receivedsignals may be raw signals or processed signals. That is, the methodsmay be applied to an output of the received signals.

FIG. 6 is a process flow diagram of a method 100 of monitoringautoregulation, in accordance with an embodiment. Some or all of thesteps of the method 100 may be implemented by the controller 16 (e.g.,the processor 24 of the controller 16) of FIG. 1, for example, todetermine the patient's autoregulation status and/or to take anappropriate action (e.g., output a visual or audible indication of theautoregulation status, block calculation and/or output of the COx, orthe like). In step 102, the controller 16 may receive the blood pressuresignal (e.g., arterial blood pressure signal). In some embodiments, thecontroller 16 may receive the blood pressure signal from the bloodpressure sensor 12, as set forth above. In step 104, the controller 16may receive the oxygen saturation signal. In some embodiments, thecontroller 16 may receive the oxygen saturation signal from the oxygensaturation sensor 14, as set forth above.

In step 106, the controller 16 may determine a change in blood pressureover a time window (e.g., approximately 0.5, 1, 2, 3, 4, 5, or moreminutes) based on the blood pressure signal. In step 108, the controller16 may determine whether the change in blood pressure is greater than athreshold (e.g., a blood pressure threshold, such as approximately 1, 2,3, 4, or 5 mmHg). If the change in blood pressure exceeds the threshold(e.g., in response to a determination that the blood pressure exceedsthe threshold), in step 110, the controller 16 may calculate a metricrelated to autoregulation status, such as the COx. In step 112, thecontroller 16 may cause the output device 18 to provide a visual oraudible indication of the patient's autoregulation status and/or theCOx. For example, the controller 16 may cause the output device 18 toprovide a numerical, graphical, symbolic, or text message indicative ofthe patient's autoregulation status and/or the COx.

If the change in blood pressure does not exceed the threshold (e.g., inresponse to a determination that the blood pressure does not exceed thethreshold), in step 114, the controller 16 may provide an appropriateindication via the output device 18. As discussed above, in certainembodiments, the controller 16 may cause the output device 18 to providean indication of a prior COx value (e.g., a most recent COx value, amost recent COx value at the same blood pressure, or an average or aweighted average of previously calculated COx values at the same bloodpressure) and/or an indication of a prior autoregulation status if thepatient's blood pressure varies by less than the threshold over theperiod of time (e.g., in response to a determination that the patient'sblood pressure varies by less than the threshold). For example, thecontroller 16 may output (e.g., cause display of) the prior COx valueuntil the blood pressure varies by more than the threshold. In some suchembodiments, the controller 16 may cause the output device 18 to providean indication that the COx value and/or autoregulation status is beingheld, that the prior COx value and/or autoregulation status is beingprovided, and/or that the COx value and/or the autoregulation status isnot being calculated.

In some such embodiments, the controller 16 may cause the output device18 to provide an indication of a time that the prior COx value and/orautoregulation status has been held and/or a time over which the COxvalue and/or the autoregulation status has not been calculated. In someembodiments, the controller 16 may cause the output device 18 to providean alert if an extended period of time (e.g., more than 5, 10, 15, 20,30, or more minutes) has passed since the blood pressure has changed bymore than the threshold (i.e., since the COx value and/or autoregulationstatus has been calculated and/or provided). As noted above, in someembodiments, the controller 16 may be configured to determine and/or tocause the output device 18 to provide an indication of the reliabilityof the provided COx value and/or autoregulation status.

In some embodiments, in step 114, the controller 16 may cause the outputdevice 18 to provide an appropriate visual or audible indication thatthe COx and/or the patient's autoregulation status is unavailable. Instep 114, the controller 16 may cause the output device 18 to display ablank display screen and/or the controller 16 may discard the COxcalculated over the period of time. In some embodiments, the controller16 may not determine and/or output the COx and/or the patient'sautoregulation status if the blood pressure does not change by more thanthe threshold (e.g., in response to a determination that the bloodpressure does not change by more than the threshold).

FIG. 7 is a process flow diagram of a method 120 of monitoringautoregulation, in accordance with an embodiment. Some or all of thesteps of the method 120 may be implemented by the controller 16 (e.g.,the processor 24 of the controller 16) of FIG. 1, for example, todetermine the patient's autoregulation status and/or to take anappropriate action (e.g., output a visual or audible indication of theautoregulation status, block calculation and/or output of the COx, orthe like). In step 122, the controller 16 may receive the blood pressuresignal (e.g., arterial blood pressure signal). In some embodiments, thecontroller 16 may receive the blood pressure signal from the bloodpressure sensor 12, as set forth above. In step 124, the controller 16may receive the oxygen saturation signal. In some embodiments, thecontroller 16 may receive the oxygen saturation signal from the oxygensaturation sensor 14, as set forth above.

In step 126, the controller 16 may determine a change in blood pressureover a time window (e.g., approximately 0.5, 1, 2, 3, 4, 5, or moreminutes) based on the blood pressure signal. In step 128, the controller16 may determine whether the change in blood pressure is greater than athreshold (e.g., a blood pressure threshold, such as approximately 1, 2,3, 4, or 5 mmHg). If the change in blood pressure exceeds the threshold(e.g., in response to a determination that the change in blood pressureexceeds the threshold), in step 130, the controller 16 may calculate ametric related to autoregulation status, such as the COx. In step 132,the controller 16 may cause the output device 18 to provide a visual oraudible indication of the patient's autoregulation status and/or theCOx. For example, the controller 16 may cause the output device 18 toprovide a numerical, graphical, symbolic, or text message indicative ofthe patient's autoregulation status and/or the COx.

If the change in blood pressure does not exceed the threshold (e.g., inresponse to a determination that the change in blood pressure does notexceed the threshold), in step 134, the controller 16 may determine achange in oxygen saturation over the time window (e.g., approximately0.5, 1, 2, 3, 4, 5, or more minutes) based on the oxygen saturationsignal. In step 136, the controller 16 may determine whether the changein oxygen saturation is greater than a threshold (e.g., an oxygensaturation threshold, such as approximately 1, 2, 3, 4, or 5 percent).If the change in oxygen saturation exceeds the threshold (e.g., inresponse to a determination that the change in oxygen saturation exceedsthe threshold), the controller 16 may determine and/or provide anindication via the output device 18 that that patient's autoregulationfunction is intact. Thus, in some embodiments, the controller 16 maydetermine and/or cause output of the patient's autoregulation statuswithout correlating the physiological signals (e.g., the blood pressuresignal and the oxygen saturation signal) and/or calculating a metric,such as the COx.

In some embodiments, if the blood pressure varies by less than thethreshold and if the oxygen saturation varies by more than the threshold(e.g., in response to such determinations), the controller 16 mayautomatically extend the period of time (e.g., continue to collect datafor an additional 0.5, 1, 2, 3, 4, or 5 minutes) prior to determiningand/or providing an indication that the patient's autoregulation isintact, in step 138. In some embodiments, if the blood pressure variesby less than the threshold and if the oxygen saturation varies by morethan the threshold (e.g., in response to such determinations), thecontroller 16 may cause the output device 18 to provide an indication ofthe reliability of the provided intact autoregulation status, asdiscussed above. In some embodiments, if the blood pressure varies byless than the threshold and if the oxygen saturation varies by more thanthe threshold (e.g., in response to such determinations), the controller16 may compare changes in the patient's regional oxygen saturationsignal (rSO₂) and arterial oxygen saturation signal (SpO₂), and thecontroller 16 may block output of the indication that patient'sautoregulation is intact if both the patient's rSO2 and the SpO2 changeby a threshold amount in the same direction (e.g., both increase or bothdecrease) over the period of time.

In some embodiments, if the blood pressure varies by less than thethreshold and if the oxygen saturation varies by less than the threshold(i.e., both parameters are generally stable) (e.g., in response to suchdeterminations), the controller 16 may cause the output device 18 toprovide an indication, in step 140. In some such embodiments, thecontroller 16 may cause the output device 18 to provide an indicationthat the COx and/or the autoregulation status cannot be reliablydetermined and/or may cause the output device 18 to provide anindication of a prior COx value and/or a prior autoregulation status, inthe manner discussed above. In some such embodiments, the controller 16may cause the output device 18 to provide an indication that the COxvalue and/or autoregulation status is being held, that the prior COxvalue and/or autoregulation status is being provided, and/or that theCOx value and/or the autoregulation status is not being calculated, forexample.

As noted above, some existing systems for monitoring autoregulation maydetermine a patient's autoregulation status based on a correlationcoefficient, such as a cerebral oximetry index (COx), a hemoglobinvolume index (HVx), a mean velocity index (Mx), and/or a pressurereactivity index (PRx). However, because many data points are requiredto reliably calculate such correlation coefficients, an extended periodof time may pass before such systems are able to provide an indicationof the patient's autoregulation status. For example, some such existingsystems collect oxygen saturation data and blood pressure data over along time window (e.g., approximately 300 seconds or more) beforecalculating and/or outputting a COx value indicative of the patient'sautoregulation status. Furthermore, multiple COx values are typicallyrequired to generate a full picture of the patient's autoregulationfunction (e.g., identify zones of blood pressures at which the patient'sautoregulation system functions properly or improperly), and thus, thelong time window may cause substantial delays in providing an indicationof the patient's autoregulation function. The long time window may alsolimit the system's ability to promptly identify changes in the patient'sautoregulation status or function.

Thus, in accordance with some embodiments of the present disclosure, apatient's autoregulation may be monitored by analyzing a relationshipbetween a change (e.g., gradient) in the patient's blood pressure (e.g.,arterial blood pressure) and a change (e.g., gradient) in the patient'soxygen saturation (e.g., regional oxygen saturation) over a period oftime (e.g., less than or approximately 30, 40, 50, 60, 90, 120, or 180seconds). For example, an intact autoregulation system will adjustcerebral blood flow such that the patient's oxygen saturation does nottrend with (e.g., change in the same direction as) a change in thepatient's blood pressure. However, an impaired autoregulation system maynot adequately adjust cerebral blood flow in response to a change in thepatient's blood pressure, and thus, a change in the patient's oxygensaturation trends with the change in the patient's blood pressure. Thus,in some embodiments, the controller 16 may be configured to process theblood pressure signal and the oxygen saturation signal to determinerespective gradients of the signals (i.e., the blood pressure gradientand the oxygen saturation gradient) over a period of time and todetermine the patient's autoregulation status based on the respectivegradients.

With reference to FIG. 4, the table 60 illustrates various oxygensaturation gradients and blood pressure gradients and correspondingautoregulation statuses. As shown in rows 62, 64, the patient'sautoregulation system may be impaired if the blood pressure gradient andthe oxygen saturation gradient trend together (e.g., change in the samedirection) over the period of time. In some cases, the patient'sautoregulation system may be intact if the blood pressure gradient andthe oxygen saturation gradient do not trend together (e.g., do notchange in the same direction, such as change in different directions, orthe blood pressure changes while the oxygen saturation remains generallystable) over the period of time.

In some embodiments, as shown in row 66, if the blood pressure isgenerally stable over the period of time, the patient's autoregulationstatus may not be reliably determined. As discussed with respect to thetable 70 of FIG. 5, it should be understood that in some embodiments, ifthe blood pressure is generally stable over the period of time and theoxygen saturation changes over the period of time, the patient'sautoregulation system may be intact because the patient's blood changesindependently of blood pressure (i.e., is not driven by changes in bloodpressure).

Thus, the controller 16 may be configured to receive and to process theblood pressure signal and the oxygen saturation signal, determine theblood pressure gradient and the oxygen saturation gradient over a periodof time, and determine the patient's autoregulation status based on thegradients. In some embodiments, the controller 16 may be configured todetermine that the patient's autoregulation system is impaired if thegradients trend together and to determine that patient's autoregulationsystem is intact if the gradients do not trend together.

In some embodiments, the controller 16 may be configured to consideradditional factors, such as whether an absolute value of the bloodpressure gradient exceeds a threshold (e.g., a blood pressure gradientthreshold) and/or whether an absolute value of the oxygen saturationgradient exceeds a threshold (e.g., an oxygen saturation gradientthreshold). In some such cases, the controller 16 may only determine thepatient's autoregulation status if the absolute value of the bloodpressure gradient exceeds the threshold. In some embodiments, thecontroller 16 may be configured to determine that the patient'sautoregulation system is impaired if the gradients trend together and ifthe respective absolute value of each gradient exceeds a respectivethreshold. In some embodiments, the controller 16 may be configured todetermine that the patient's autoregulation system is intact if theblood pressure gradient and the oxygen saturation gradient do not trendtogether (e.g., the respective absolute value of each gradient exceeds arespective threshold and the gradients are in different directions, theabsolute value of the blood pressure gradient exceeds the threshold andthe absolute value of the oxygen saturation gradient does not exceed thethreshold, and/or the absolute value of the blood pressure gradient doesnot exceed the threshold and the absolute value of the oxygen saturationgradient exceeds the threshold).

With the foregoing in mind, FIG. 8 is a flow chart illustrating a method150 for monitoring autoregulation based on a relationship betweengradients of oxygen saturation and blood pressure (e.g., gradient-basedmetric), in accordance with the present disclosure. As shown in FIG. 8,in step 152, the controller 16 may receive the blood pressure signal(e.g., arterial blood pressure signal). In some embodiments, thecontroller 16 may receive the blood pressure signal from the bloodpressure sensor 12, as set forth above. In step 154, the controller 16may receive the oxygen saturation signal. In some embodiments, thecontroller 16 may receive the oxygen saturation signal from the oxygensaturation sensor 14, as set forth above.

In step 156, the controller 16 may determine a blood pressure gradientover a period of time (e.g., a time window of less than or approximately30, 40, 50, 60, 90, 120, or 180 seconds) based on the blood pressuresignal. In step 158, the controller 16 may determine an oxygensaturation gradient (e.g., a change in oxygen saturation) over theperiod of time based on the oxygen saturation signal. In step 160, thecontroller 16 may determine a relationship between the blood pressuregradient and the oxygen saturation gradient. For example, the controller16 may determine whether the gradients trend together (e.g., whetherboth gradients are negative or positive) over the period of time. Asdiscussed above, gradients that trend together may be indicative ofimpaired autoregulation status, while gradients that do not trendtogether may be indicative of intact autoregulation status.

In some embodiments, as shown in a dotted line, in step 162, thecontroller 16 may be configured to instruct the output device 18 toprovide an indication of the patient's autoregulation status based onthe relationship between the blood pressure gradient and the oxygensaturation gradient. For example, the controller 16 may instruct theoutput device 18 to provide an indication that the patient'sautoregulation status is impaired if the gradients trend together and/oran indication that the patient's autoregulation status is intact if thegradients do not trend together. In some embodiments, the output device18 includes a display to display a text message, a symbol, or othervisual representation of the patient's autoregulation status and/or theoutput device 18 includes a speaker to provide sounds in accordance withthe patient's autoregulation status.

As discussed above, in certain embodiments, the controller 16 may beconfigured to consider additional factors to determine the patient'sautoregulation status and/or prior to outputting the indication. Asshown, in certain embodiments, the controller 16 may compare the changein blood pressure and the change in oxygen saturation to respectivethresholds to determine the patient's autoregulation status. Forexample, in step 164 of the illustrated method 150, the controller 16may determine whether an absolute value of the blood pressure gradientover the period of time exceeds a threshold (e.g., a predeterminedthreshold, such as 0.1, 0.5, 1, 2, 3, 4, 5, or more mmHg). In step 166,if the absolute value of the blood pressure gradient does not exceed thethreshold (e.g., in response to a determination that the absolute valueof the blood pressure gradient does not exceed the threshold), thecontroller 16 may not determine and/or output the patient'sautoregulation status based on the gradients over the current period oftime, but instead may hold a prior determination (e.g., anautoregulation status determined in a prior time window and/or at asimilar blood pressure). In step 162, the controller 16 may instruct theoutput device 18 to provide an autoregulation status indication based onthe prior determination. In some embodiments, the controller 16 mayinstruct the output device 18 to provide an indication that thepatient's autoregulation status could not be reliably determined and/orthat the prior determination is provided on the output device 18.

If the absolute value of the blood pressure gradient exceeds thethreshold (e.g., in response to a determination that the absolute valueof the blood pressure gradient exceeds the threshold), the controller 16may determine whether an absolute value of the oxygen saturationgradient over the period of time exceeds a threshold (e.g.,predetermined threshold, such as 0.1, 0.5, 1, 2, 3, 4, 5, or morepercent), in step 168. In some such embodiments, if the absolute valueof the oxygen saturation gradient does not exceed the threshold (e.g.,in response to a determination that the absolute value of the oxygensaturation gradient does not exceed the threshold), the controller 16may determine that the patient's autoregulation system is intact, instep 170. Following such a determination, the controller 16 may instructthe output device 18 to provide an indication that the patient'sautoregulation status is intact, in step 162.

In step 172, if the absolute value of the blood pressure gradient andthe absolute value of the oxygen saturation gradient exceed therespective thresholds (e.g., in response to such determinations), thecontroller 16 may determine the patient's autoregulation status (e.g.,impaired or intact) based on the relationship between the gradientsdetermined in step 160, and the controller 16 may instruct the outputdevice 18 to provide an output indicative of the patient'sautoregulation status based on the relationship between the gradients,in step 162. In such cases, the controller 16 may instruct the outputdevice 18 to provide an indication that the patient's autoregulationstatus is impaired if the gradients trend together and/or an indicationthat the patient's autoregulation status is intact if the gradients donot trend together. As noted above with respect to FIG. 5, in someembodiments, if the blood pressure gradient does not exceed thethreshold and the oxygen saturation gradient exceeds the threshold overthe period of time (e.g., in response to such determinations), thecontroller 16 may be configured to determine that the patient'sautoregulation system is intact and/or to instruct the output device 18to provide an indication.

FIG. 9A is an example of a graph 180 illustrating an oxygen saturationsignal 182 and a blood pressure signal 184 over a period of time 186.FIG. 9B is an example of a graph 188 illustrating an oxygen saturationgradient 190 (e.g., a gradient of the oxygen saturation signal 182) anda blood pressure gradient 192 (e.g., a gradient of the blood pressuresignal 184) over the period of time 186. As discussed above, thecontroller 16 may be configured to receive the oxygen saturation signal182 and the blood pressure signal 184 and determine respective gradients190, 192 over the period of time 186. The relationship between thegradients 190, 192 may be indicative of the patient's autoregulationstatus and may be used to generate an indication, such as visual oraudible indication, of the patient's autoregulation status via theoutput device 18. For example, FIG. 9C is an example of a graph 194illustrating a representation of the patient's autoregulation statusover the period of time 186 based on the gradients of FIG. 9B. In theillustrated embodiment, the lighter colored regions 196 represent intactautoregulation and the darker colored regions 198 represent impairedautoregulation. In some embodiments, the graph 194 may be provided forvisualization by an operator via a display of the output device 18.

In some embodiments, the controller 16 may be configured to determine aconfidence level (e.g., quality metric) associated with the determinedautoregulation status. In some embodiments, the confidence level mayvary based on the absolute value of one or both gradients. In general,greater absolute values over the period of time may correspond togreater confidence in the determined autoregulation status. For example,if the patient's blood pressure and oxygen saturation both changesubstantially in the same direction over the period of time, theconfidence in the determination that the patient's autoregulationfunction is impaired is generally higher than if the blood pressure andoxygen saturation both change in the same direction by a smallerabsolute value. The controller 16 may be configured to determine and toassign a confidence level (e.g., numerical value on a scale, such as ascale of 1 to 10 or 1 to 100, or a non-numerical indicator, such ashigh, intermediate, or low) based on the absolute values of thegradients, such as based on whether the absolute values of the gradientsexceed various thresholds. In some embodiments, the controller 16 may beconfigured to instruct the output device 18 to provide a visual oraudible indication of the confidence level (e.g., the numerical value ornon-numerical indicator).

Additionally or alternatively, in some embodiments, a correlationcoefficient or a significance value (p value) of a fitted line used tocalculate the blood pressure gradient or the oxygen saturation gradientin the period of time may be used as a confidence metric. In particular,the p value may enable the controller 16 to determine whether thegradients are reliable or unreliable. For example, the p value mayenable the controller 16 to identify certain portions of the signalsthat are adversely affected by noise, and therefore, unreliable. In someembodiments, the controller 16 maybe configured to calculate the p valueand to remove unreliable data based on the p value.

Additionally or alternatively, in some embodiments, the confidence levelmay be determined and/or adjusted based on prior gradients and/or priorautoregulation status determinations (e.g., in prior periods of time orprior time windows). For example, respective gradients across the sameblood pressures over multiple time windows may be compared and used todetermine whether the gradients and/or autoregulation statusdetermination in the current time window agree with the prior gradientsand/or prior autoregulation status determinations. If the informationagrees, the confidence level may be high or increased, while if theinformation does not agree, the confidence level may be low ordecreased. In some embodiments, the gradients across multiple timewindows may be averaged to generate average gradients (e.g., an averageblood pressure gradient and an average oxygen saturation gradient), andthe average gradients may be used to determine the patient'sautoregulation status in the manner set forth above with respect toFIGS. 1-9. Additional techniques for processing and/or consideringinformation across multiple time windows are discussed in more detailbelow.

In some embodiments, the controller 16 may be configured to determinethe patient's autoregulation status without calculating a correlationcoefficient, such as a COx, HVx, Mx, and/or PRx. In some embodiments,the controller 16 may be configured to determine the patient'sautoregulation status based on the gradients over the period of time incombination with one or more correlation coefficients calculatedsimultaneously or at different times. For example, the controller 16 maybe configured to utilize the gradients at the beginning of a monitoringsession (e.g., during first 30, 40, 50, 60, 90, 120, or 180 seconds ofthe signals) to quickly provide an indication of the patient'sautoregulation status, and then subsequently calculate and utilize theCOx in addition to or in lieu of the gradients. Such embodiments mayadvantageously enable efficient determination and output of anindication of the patient's autoregulation status at the beginning ofthe patient monitoring session without the extended delay that may occurin typical systems that determine autoregulation status based only onthe correlation coefficients. Furthermore, when the gradients are usedin conjunction with one or more correlation coefficients, thecombination of measurements may enable the controller 16 to quicklyidentify sudden changes in the patient's autoregulation status and/orprovide increased confidence in the determination of the patient'sautoregulation status.

The patient's autoregulation status may be monitored over multiple timewindows and across various blood pressures, and this information may beused to generate a full picture of the patient's autoregulationfunction. In general, a patient's autoregulation system may typicallyfunction well over a certain range of blood pressures. Accordingly, eachpatient typically exhibits at least three autoregulation zones: a lowerimpaired autoregulation zone associated with relatively low bloodpressures at which the patient's autoregulation function is impaired, anintact autoregulation zone associated with intermediate blood pressuresat which the patient's autoregulation system works properly, and anupper impaired autoregulation zone associated with relatively high bloodpressures at which the patient's autoregulation function is impaired.For example, although the blood pressures at which the autoregulationsystem functions properly may vary by patient, a particular patient mayexhibit a lower impaired autoregulation zone associated with relativelylow blood pressures of less than approximately 60 mmHg at which thepatient's autoregulation function is impaired, an intact autoregulationzone associated with intermediate blood pressures between approximately60 and 150 mmHg at which the patient's autoregulation system worksproperly, and an upper impaired autoregulation zone associated withrelatively high blood pressures above approximately 150 mmHg at whichthe patient's autoregulation function is impaired.

In some embodiments of the present disclosure, the controller 16 maydetermine a current instantaneous autoregulation status, S(i), for eachblood pressure value based on the relationship between the bloodpressure gradient and the oxygen saturation gradient in a time window,such as in the manner set forth above with respect to FIGS. 8 and 9, forexample. In some embodiments, the controller 16 may determine aconfidence level of the current instantaneous autoregulation status. Thecurrent instantaneous autoregulation status and/or the confidence levelof the current instantaneous autoregulation status may be stored, suchas in the memory 26.

For each blood pressure, the current instantaneous autoregulationstatus, S(i), and a previously reported instantaneous autoregulationstatus, rS(i−1), are considered together by the controller 16 togenerate an updated autoregulation status, rS(i), which may then bereported to the output device 18 to provide an indication of thepatient's current autoregulation status. Thus, the current instantaneousautoregulation status, S(i), may be modified, adjusted, or discarded inview of prior data and/or prior autoregulation status determination(s).

For example, in certain embodiments, for each blood pressure, thecurrent instantaneous autoregulation status, S(i), may be compared tothe previously reported instantaneous autoregulation status, rS(i−1). IfS(i) and rS(i−1) agree (e.g., both indicate intact autoregulation orboth indicate impaired autoregulation at the blood pressure), then rS(i)is set to S(i) and a high confidence level is assigned to and/orreported (e.g., via the output device 18) with rS(i). If S(i) andrS(i−1) do not agree (e.g., one indicates intact autoregulation and oneindicates impaired autoregulation at the blood pressure), then thecontroller 16 may check a confidence level associated with rS(i−1). Ifthe confidence level associated with rS(i−1) is high (e.g., above athreshold), then rS(i) is set to rS(i−1). If the confidence levelassociated with rS(i−1) is low (e.g., below the threshold), then thecontroller 16 may evaluate the previously reported instantaneousautoregulation statuses at neighboring blood pressures and may set rS(i)based on some rS(i) indicators or values previously determined atneighboring blood pressures. For example, if the patient'sautoregulation status is impaired at neighboring blood pressures locatedabove and below the current blood pressure, then rS(i) may be set toindicate impaired autoregulation status. In some such embodiments, theconfidence level associated with rS(i) may be reduced or set to low.

To facilitate generation of the full picture of the patient'sautoregulation function and to facilitate reliable reporting of thepatient's autoregulation status across all blood pressures, theautoregulation status and/or corresponding confidence levels atneighboring blood pressures may be considered by the controller 16 invarious other situations. In some embodiments, if there is no prior datafor a particular blood pressure, if the confidence level of the currentinstantaneous autoregulation status, S(i), at a particular bloodpressure is below a predetermined threshold, and/or if conflictingautoregulation status indications at a particular blood pressure oracross nearby blood pressures exist, the controller 16 may consider thepreviously reported autoregulation statuses at neighboring bloodpressures and/or the corresponding confidence levels. For example, if acurrent instantaneous autoregulation status, S(i), at 100 mmHg indicatesthat the patient's autoregulation status is impaired, but previouslyreported instantaneous autoregulation statuses at 95 mmHg and at 105mmHg indicate intact autoregulation with higher confidence, thecontroller 16 may discard S(i) and/or set rS(i) to provide an indicationof intact autoregulation at 100 mmHg. Thus, the controller 16 may beconfigured to remove anomalous regions or data.

In some embodiments, if there is no prior data for a particular bloodpressure, then the current instantaneous autoregulation status, S(i),will be stored, such as in the memory device 26 or buffer, until acertain number (e.g., 2, 3, 4, 5 or more) of current instantaneousautoregulation statuses, S(i), at the particular blood pressure aredetermined (e.g., via assessment of the blood pressure gradient andoxygen saturation gradient over multiple time windows). In someembodiments, the controller 16 may not identify or provide an indicationthat the particular blood pressure is associated with an intact orimpaired autoregulation status until at least two S(i) indications atthe particular blood pressure are obtained and agree with one another.Additionally or alternatively, in some embodiments, prior data may bedown weighted and/or discarded based on age. In some embodiments, aconfidence level associated with a previously reported instantaneousautoregulation status, rS(i−1), may be reduced based on age.

With the foregoing in mind, FIG. 10 is a flow chart illustrating amethod 200 for monitoring autoregulation, in accordance with the presentdisclosure. In step 202, the controller 16 may receive the bloodpressure signal (e.g., arterial blood pressure signal). In someembodiments, the controller 16 may receive the blood pressure signalfrom the blood pressure sensor 12, as set forth above. In step 204, thecontroller 16 may receive the oxygen saturation signal. In someembodiments, the controller 16 may receive the oxygen saturation signalfrom the oxygen saturation sensor 14, as set forth above.

In step 206, the controller 16 may determine a blood pressure gradientover a time window (e.g., less than or approximately 30, 40, 50, 60, 90,120, or 180 seconds) based on the blood pressure signal. In step 208,the controller 16 may determine an oxygen saturation gradient (e.g., achange in oxygen saturation) over the time window based on the oxygensaturation signal. In step 210, the controller 16 may determine thepatient's autoregulation status based on a relationship between theblood pressure gradient and the oxygen saturation gradient in the mannerdescribed above with respect to FIGS. 8 and 9, for example. In certainembodiments, for each blood pressure in the time window, the controller16 may set a current instantaneous autoregulation status, S(i), tointact or impaired based on the relationship between the gradientsand/or may assign a corresponding confidence level.

In step 212, the controller 16 may access a previously reportedinstantaneous autoregulation status, rS(i−1), which may be stored in thememory device 26, for example. In step 214, for each blood pressure, thecurrent instantaneous autoregulation status, S(i), is compared to thepreviously reported instantaneous autoregulation status, rS(i−1), by thecontroller 16. In step 216, if S(i) and rS(i−1) agree (e.g., in responseto a determination that both indicate intact autoregulation or bothindicate impaired autoregulation at the blood pressure), then thecontroller 16 may generate an updated autoregulation status, rS(i), bysetting rS(i) to S(i). In some such embodiments, the controller 16 mayassign and/or report a high confidence level (e.g., via the outputdevice 18) with rS(i). In step 218, the controller 16 may instruct theoutput device 18 to provide an indication of rS(i).

In step 220, if S(i) and rS(i−1) do not agree (e.g., in response to suchdetermination), then the controller 16 may check a confidence levelassociated with rS(i−1). In step 122, if the confidence level associatedwith rS(i−1) is high (e.g., in response to a determination that rS(i−1)is above a threshold), then rS(i) is set to rS(i−1) and reported in step118. In step 224, if the confidence level associated with rS(i−1) is low(e.g., in response to a determination that rS(i−1) is below thethreshold), then the controller 16 may evaluate the previously reportedinstantaneous autoregulation statuses at neighboring blood pressures andmay set rS(i) based on the neighboring blood pressures.

As discussed above, various additional post-processing techniques may beapplied to determine and report the patient's autoregulation status. Forexample, the controller 16 may be configured to utilize prior data atneighboring blood pressures in any of a variety of manners, such as toremove anomalous regions. In some embodiments, the controller 16 may notdetermine or provide an indication of autoregulation status until aminimum number of data points at a given blood pressure are obtained.Thus, according to the method 200 set forth in FIG. 10, the currentinstantaneous autoregulation status, S(i), determined via analysis ofthe gradients in the time window may be modified, adjusted, or discardedin view of prior data and/or prior autoregulation statusdetermination(s) at the same or neighboring blood pressures. The updatedautoregulation status, rS(i), generated via the method 200 and reported(e.g., via the output device 18) in step 218 may provide a reliableindication of autoregulation status and may facilitate generation of afull picture of the patient's autoregulation function over time. Theupdated autoregulation status 218 may be stored in the memory device 26for subsequent use (e.g., to modify future instantaneous autoregulationstatus(es) in the manner set forth in steps 212-224).

FIG. 11 is an example of a graph 230 that may be generated via themethod 200 of FIG. 10. The graph 230 illustrates autoregulation functionacross various blood pressures 232. In the illustrated embodiment, thelighter colored region 234 (e.g., blood pressure range) represents anintact autoregulation zone and the darker colored regions 236 (e.g.,blood pressure ranges) represent impaired autoregulation zones. Tofacilitate discussion, the graph 230 also illustrates a blood pressuresignal 238 and an oxygen saturation signal 240 obtained over time 242that were used to generate the graph 230. In some embodiments, the graph230 may be provided for visualization by an operator via the outputdevice 18. Additionally or alternatively, in some embodiments, thecontroller 16 may calculate and/or instruct the output device 18 toprovide other indications based on the graph 230, such as a numericalindication of an upper limit of autoregulation (ULA) value and/or alower limit of autoregulation (LLA) that approximately define an upperand a lower blood pressure boundary, respectively, of the intactautoregulation zone (e.g., the lighter color region 234) within whichautoregulation is generally intact and functions properly.

As noted above, the method 200 set forth in FIG. 10 may be used todetermine the patient's autoregulation status and/or to generate a fullpicture of the patient's autoregulation function based on variouscoefficients or indices related to autoregulation, such as COx, Mx, HVx,and PRx. To facilitate discussion, the COx is provided as an example. Insome embodiments, the controller 16 may determine a COx value based onthe linear correlation between blood pressure measurements of a bloodpressure signal and oxygen saturation measurements of an oxygensaturation signal over a period of time (e.g., a time window, such asapproximately 300 seconds). As discussed above with respect to FIG. 2,the linear correlation may be based on a Pearson coefficient, which maybe defined as the covariance of the measured blood pressure (e.g., meanarterial blood pressure) and oxygen saturation divided by the product oftheir standard deviations. The result of the linear correlation may be aregression line between oxygen saturation measurements and bloodpressure measurements, which is then used to determine the patient'sautoregulation status. The controller 16 may determine a value of theCOx, which may be between −1 and 1, inclusive, where −1 represents totalnegative correlation, +1 represents total positive correlation, and 0represents the absence of correlation between the blood pressuremeasurements and the oxygen saturation measurements. Thus, COx valuesbetween −1 and 0 may suggest that cerebral autoregulation is workingproperly, while COx values between 0 and 1 may suggest that the cerebralautoregulation is impaired. In some cases, a predetermined thresholdbetween 0 and 1 may be utilized to determine whether the patient'sautoregulation is impaired. For example, in some embodiments, thecontroller 16 may be configured to determine that the patient'sautoregulation is impaired when the COx value is greater than 0.1, 0.2,0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

In some embodiments, the controller 16 may determine a currentinstantaneous COx value, COx(i), for each blood pressure in the timewindow. The controller 16 may be configured to adapt steps 212-224 ofthe method 200 of FIG. 10 to adjust the current instantaneous COx value,COx(i), based on prior COx value(s), rCOx(i−1), to generate an updatedCOx value, rCOx(i), at the particular blood pressure. For example, thecontroller 16 may access a prior COx value, compare the currentinstantaneous COx value to the prior COx value, report the currentinstantaneous COx value if the current instantaneous COx value and theprior COx value agree (e.g., in response to a determination that bothindicate intact autoregulation, both indicate impaired autoregulation,and/or are within a predetermined percentage of one another), report theprior COx value if the current instantaneous COx value and the prior COxvalue disagree and if the prior COx value has a high confidence level(e.g., above a threshold) (e.g., in response to such determinations),and/or consider the COx values or autoregulation statuses at neighboringblood pressures if the current COx value and the prior COx valuedisagree and if the prior COx value has a low confidence level (e.g.,below the threshold) (e.g., in response to such determinations). Themethod 200 may be applied to numerical COx values or to statusindications (e.g., intact or impaired) based on COx values. For example,COx(i) may be a numerical COx value, such as 0.8, or a status indicator,such as impaired autoregulation status.

In another method 250 set forth in FIG. 7, the current instantaneous COxvalue, COx(i), may be combined with the previously reportedinstantaneous COx value, rCOx(i−1), to generate the updated COx value,rCOx(i), for the particular blood pressure. In step 252, the controller16 may receive the blood pressure signal (e.g., arterial blood pressuresignal). In some embodiments, the controller 16 may receive the bloodpressure signal from the blood pressure sensor 12, as set forth above.In step 254, the controller 16 may receive the oxygen saturation signal.In some embodiments, the controller 16 may receive the oxygen saturationsignal from the oxygen saturation sensor 14, as set forth above.

In step 256, the controller 16 may determine a COx value e.g., between−1 and 1, inclusive) based on the linear correlation between bloodpressure measurements of the blood pressure signal and the oxygensaturation measurements of the oxygen saturation signal over a period oftime (e.g., a time window, such as approximately 300 seconds), and thecontroller 16 may set a current instantaneous COx value, COx(i), foreach blood pressure in the time window.

In step 258, the controller 16 may access a previously reportedinstantaneous COx value, rCOx(i−1), which may be stored in the memorydevice 26, for example. In step 260, the controller 16 may combineCOx(i) and rCOx(i−1) for a particular blood pressure to generate anupdated COx value, rCOx(i), for the particular blood pressure. In someembodiments, the controller may combine COx(i) and rCOx(i−1) via thefollowing equation:rCO_(x)(i)=w*CO_(x)(i)+(1−w)*rCO_(x)(i−1)  (Equation 1)where w is a weighting factor. In some embodiments, the weighting factormay be based on a confidence level associated with the COx value. Insome embodiments, the weighting factor may be adjusted based on the ageof rCOx(i−1).

In step 260, the controller 16 may apply various additional processingtechniques to determine and/or report the patient's autoregulationstatus. For example, if there is no prior data for a particular bloodpressure, if the confidence level of the current instantaneous COxvalue, COx(i), at a particular blood pressure is below a predeterminedthreshold, and/or if conflicting COx values and/or autoregulation statusindications at a particular blood pressure or across nearby bloodpressures exist (e.g., in response to such determination(s)), thecontroller 16 may consider the previously reported COx values and/orautoregulation statuses at neighboring blood pressures and/or thecorresponding confidence levels. For example, the controller 16 may beconfigured to consider such information to remove anomalous data. Insome embodiments, the controller 16 may not determine or provide anindication of autoregulation status until a minimum number of datapoints and/or multiple COx values at a given blood pressure areobtained. In some embodiments, a confidence level and/or the weightingfactor associated with a previously reported instantaneous COx value,rCOx(i−1), may be reduced based on age. Additionally, if multiple datapoints at a particular blood pressure are obtained over the period oftime, the data points obtained at the beginning of the period of timemay be down weighted, or the period of time over which the data pointsare collected may vary based on a number of data points at theparticular blood pressure to facilitate efficient calculation of COx(i)and rCOx(i) at each blood pressure.

In step 262, the controller 16 may instruct the output device 18 toprovide an indication of rCOx(i). In some embodiments, the controller 16may utilize the method 250 to generate a graph similar to the graph 230shown in FIG. 11 that illustrates autoregulation function across variousblood pressures. The controller 16 may instruct the output device 18 toprovide the graph or any of a variety of other indications, such as anumerical indication of an upper limit of autoregulation (ULA) valueand/or a lower limit of autoregulation (LLA) that approximately definean upper and a lower blood pressure boundary, respectively, of theintact autoregulation zone within which autoregulation is generallyintact and functions properly. Thus, according to the method 250 setforth in FIG. 12, the current instantaneous COx value, COx(i), may bemodified, adjusted, or discarded in view of prior data and/or priorautoregulation status determination(s) at the same or neighboring bloodpressures. The updated autoregulation status, rCOx(i), generated via themethod 250 and reported (e.g., via the output device 18) in step 262 mayprovide a reliable indication of autoregulation status and mayfacilitate generation of a full picture of the patient's autoregulationfunction over time.

It should also be understood that the method 250 may be adapted tomonitor the patient's autoregulation status with other correlationcoefficients, such as HVx, Mx, and/or PRx. Furthermore, the gradients,COx, HVx, Mx, PRx, or any other suitable indicator may be utilized incombination to monitor the patient's autoregulation status. For example,the controller 16 may carry out the method 200 using the gradients andmay carry out method 250 using the COx values simultaneously to enablerelatively efficient evaluation of the patient's autoregulation statusand recognition of changes via the gradients, as well as increasedconfidence in the determined autoregulation status via the use ofmultiple measurement techniques. If the autoregulation status determinedbased on the gradients agrees with the autoregulation status determinedbased on the COx value, then the confidence level in the determinationmay be relatively higher than if only one measurement technique wereutilized. The confidence level may then be utilized in subsequentcalculations or assessments of the patient's autoregulation status inthe manner set forth above in FIGS. 10 and 12, thereby increasing thereliability and confidence of the determined autoregulation state,autoregulation zones, and other related information.

While the disclosure may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the embodiments provided hereinare not intended to be limited to the particular forms disclosed.Rather, the various embodiments may cover all modifications,equivalents, and alternatives falling within the spirit and scope of thedisclosure as defined by the following appended claims. Further, itshould be understood that certain elements of the disclosed embodimentsmay be combined or exchanged with one another.

What is claimed is:
 1. A system for monitoring autoregulation, thesystem comprising: an oxygen saturation sensor configured to obtain anoxygen saturation signal indicative of an oxygen saturation of apatient; and a controller comprising one or more processors configuredto: receive the oxygen saturation signal; receive a blood pressuresignal indicative of a blood pressure of the patient; determine anoxygen saturation gradient based on the oxygen saturation signal over aperiod of time; determine a blood pressure gradient based on the bloodpressure signal over the period of time; determine an absolute value ofthe blood pressure gradient; in response to determining that theabsolute value of the blood pressure gradient exceeds a blood pressuregradient threshold in a first instance: determine a cerebral oximetryindex (COx) value based on the blood pressure signal and the oxygensaturation signal; and monitor an autoregulation status of the patientbased on the COx value and a relationship between the oxygen saturationgradient and the blood pressure gradient; and in response to determiningthat the absolute value of the blood pressure gradient does not exceedthe blood pressure gradient threshold in a second instance, monitor theautoregulation status of the patient based on the relationship betweenthe oxygen saturation gradient and the blood pressure gradient withoutdetermining the COx value.
 2. The system of claim 1, wherein the one ormore processors are configured to: determine an absolute value of theoxygen saturation gradient; and determine that an autoregulation systemof the patient is impaired if the absolute value of the oxygensaturation gradient exceeds an oxygen saturation gradient threshold, ifthe absolute value of the blood pressure gradient exceeds a bloodpressure gradient threshold, and if the oxygen saturation gradient andthe blood pressure gradient trend together over the period of time. 3.The system of claim 2, wherein the one or more processors are configuredto determine a confidence level associated with the autoregulationstatus based on the absolute value of the blood pressure gradient, theabsolute value of the oxygen saturation gradient, or a combinationthereof.
 4. The system of claim 1, wherein the one or more processorsare configured to present an indication related to the autoregulationstatus of the patient on a display.
 5. The system of claim 1, whereinthe one or more processors are configured to determine theautoregulation status without calculating a correlation coefficientbetween the oxygen saturation signal and the blood pressure signal. 6.The system of claim 1, wherein the one or more processors are configuredto: set a current instantaneous autoregulation status for a first bloodpressure monitored over the period of time based on the determinedautoregulation status; modify the current instantaneous autoregulationstatus based on a prior instantaneous autoregulation status to generatean updated autoregulation status for the first blood pressure; andpresent an indication of the updated autoregulation status via adisplay.
 7. The system of claim 1, wherein the one or more processorsare configured to: determine an absolute value of the oxygen saturationgradient; and determine that an autoregulation system of the patient isintact if the absolute value of the oxygen saturation gradient exceedsan oxygen saturation gradient threshold over the period of time and ifthe absolute value of the blood pressure gradient does not exceed ablood pressure gradient threshold over the period of time.
 8. A systemfor monitoring autoregulation, the system comprising: a memory encodingone or more processor-executable instructions; and a controllercomprising one or more processors configured to access and execute theone or more instructions encoded by the memory, wherein theinstructions, when executed cause the one or more processors to: receivean oxygen saturation signal indicative of an oxygen saturation of apatient; receive a blood pressure signal indicative of a blood pressureof the patient; determine an oxygen saturation gradient based on theoxygen saturation signal over a period of time; determine a bloodpressure gradient based on the blood pressure signal over the period oftime; determine an absolute value of the blood pressure gradient; inresponse to determining that the absolute value of the blood pressuregradient exceeds a blood pressure gradient threshold in a firstinstance: determine a cerebral oximetry index (COx) value based on theblood pressure signal and the oxygen saturation signal; and monitor anautoregulation status of the patient based on the COx value and arelationship between the oxygen saturation gradient and the bloodpressure gradient; in response to determining that the absolute value ofthe blood pressure gradient does not exceed the blood pressure gradientthreshold in a second instance, monitor the autoregulation status of thepatient based on the relationship between the oxygen saturation gradientand the blood pressure gradient without determining the COx value; andpresent, via a display, an indication related to the autoregulationstatus.
 9. The system of claim 8, wherein the one or more processors areconfigured to: determine an absolute value of the oxygen saturationgradient; and determine that an autoregulation system of the patient isimpaired if the absolute value of the oxygen saturation gradient exceedsan oxygen saturation gradient threshold, if the absolute value of theblood pressure gradient exceeds a blood pressure gradient threshold, andif the oxygen saturation gradient and the blood pressure gradient trendtogether over the period of time.
 10. The system of claim 9, wherein theblood pressure gradient threshold is between two millimeters of mercury(mmHg) and four mmHg.
 11. The system of claim 9, wherein the one or moreprocessors are configured to determine a confidence level associatedwith the autoregulation status based on the absolute value of the bloodpressure gradient, the absolute value of the oxygen saturation gradient,or a combination thereof.
 12. The system of claim 8, wherein the one ormore processors are configured to determine the autoregulation status ofthe patient without calculating a correlation coefficient between theoxygen saturation signal and the blood pressure signal.
 13. The systemof claim 8, wherein the one or more processors are configured to: set acurrent instantaneous autoregulation status for a first blood pressuremonitored over the period of time based on the determined autoregulationstatus; modify the current instantaneous autoregulation status based ona prior instantaneous autoregulation status to generate an updatedautoregulation status for the first blood pressure; and present anindication of the updated autoregulation status via the display.
 14. Thesystem of claim 13, wherein the one or more processors are configuredto: generate multiple updated autoregulation statuses across multipleblood pressures based on respective modified instantaneousautoregulation statuses; and generate a graph indicative of the bloodpressures at which an autoregulation system of the patient is intact andimpaired based on the multiple updated autoregulation statuses.
 15. Thesystem of claim 13, wherein the prior instantaneous autoregulationstatus corresponds to a neighboring blood pressure different from thefirst blood pressure.
 16. The system of claim 8, wherein the one or moreprocessors are configured to: determine an absolute value of the oxygensaturation gradient; and determine that an autoregulation system of thepatient is intact if the absolute value of the oxygen saturationgradient exceeds an oxygen saturation gradient threshold over the periodof time and if the absolute value of the blood pressure gradient doesnot exceed a blood pressure gradient threshold over the period of time.17. A method for monitoring autoregulation, the method comprising:receiving, by one or more processors and from one or more sensors, anoxygen saturation signal indicative of an oxygen saturation of apatient; receiving, by the one or more processors and from the one ormore sensors, a blood pressure signal indicative of a blood pressure ofthe patient; determining, by the one or more processors, an oxygensaturation gradient based on the oxygen saturation signal over a periodof time; determining, by the one or more processors, a blood pressuregradient based on the blood pressure signal over the period of time;determining, by the one or more processors, an absolute value of theblood pressure gradient; in response to determining that the absolutevalue of the blood pressure gradient exceeds a blood pressure gradientthreshold in a first instance: determining, by the one or moreprocessors, a cerebral oximetry index (COx) value based on the bloodpressure signal and the oxygen saturation signal; and monitoring, by theone or more processors, an autoregulation status of the patient based onthe COx value and a relationship between the oxygen saturation gradientand the blood pressure gradient; and in response to determining that theabsolute value of the blood pressure gradient does not exceed the bloodpressure gradient threshold in a second instance, monitoring, by the oneor more processors, the autoregulation status of the patient based onthe relationship between the oxygen saturation gradient and the bloodpressure gradient without determining the COx value.
 18. The method ofclaim 17, further comprising: determining, by the one or moreprocessors, an absolute value of the oxygen saturation gradient; anddetermining, by the one or more processors, that an autoregulationsystem of the patient is impaired in response to a determination thatthe absolute value of the oxygen saturation gradient exceeds an oxygensaturation gradient threshold, that the absolute value of the bloodpressure gradient exceeds a blood pressure gradient threshold, and thatthe oxygen saturation gradient and the blood pressure gradient trendtogether over the period of time.
 19. The method of claim 17, furthercomprising: setting, by the one or more processors, a currentinstantaneous autoregulation status for a first blood pressure monitoredover the period of time based on the determined autoregulation status;modifying, by the one or more processors, the current instantaneousautoregulation status based on a prior instantaneous autoregulationstatus to generate an updated autoregulation status for the first bloodpressure; and presenting, by the one or more processors, an indicationof the updated autoregulation status via a display.
 20. The method ofclaim 17, further comprising: determining, by the one or moreprocessors, an absolute value of the oxygen saturation gradient; anddetermining, by the one or more processors, that an autoregulationsystem of the patient is intact if the absolute value of the oxygensaturation gradient exceeds an oxygen saturation gradient threshold overthe period of time and if the absolute value of the blood pressuregradient does not exceed a blood pressure gradient threshold over theperiod of time.